Goodbye, stars

For me, reading a book on a scientific subject is not only an intellectual process, but an almost visceral one as well. At some gut level, I really, really want to get it. In the end, I think that's what makes it so much fun.

A case in point is the current book I'm reading - I'm about a third through the one about an ultimate theory of time, "From Eternity to Here" by Sean Carroll - which is light on equations (thankfully) but quite a bit deeper than many a popular-science effort. It is well-written, smart, clever and lucid about some really important mysteries that today's scientists are struggling to understand. It is slow-going for me, but only because most of its hundreds of end-notes are just as interesting as the text. Lots of paging back the forth.

But, for this reader, a lack of mathematical savvy still can bewilder. For instance, we all know that science has pretty much pinpointed the age of the (observable) universe at about 13.7 billion years. So that means that with even the perfect telescope, the farthest we could see is 13.7 billion light years. Turning the telescope around 180 degrees, we could see 13.7 billion light years in the opposite direction. So - the book uses the shorthand of 14 billion years - the greatest extent of the universe we will ever be able to see of the observable universe should be 28 billion light years across.

But, darn it, the universe is expanding. Particularly, Carroll notes (literally, in an end-note), it is being accelerated by dark energy. (Which apparently is really hard to talk about without recourse to mathematical equations.) (Metaphors involving rubber bands really don't cut it.) Anyway, according to this same end-note, "the farthest point that was ever within our observational patch of universe is now 46 billion light years distant."

OK. But what about some galaxy that sometime in the past - say 4.5 billion years ago, when our sun and planets formed - was just about to move out of our sight - irrevocably and forever beyond light's ability to reach us? Presumably that last light has been traveling toward us ever since, and will reach us, when it does, whenever it does. And then, it will wink out.

Presumably, stars and their galaxies are winking out all the time. We just can't see them pass beyond our view because we can't see far enough. But shouldn't a stream of light from a soon-to-disappear star, much like a finite rope, come to an end in our view as well? Or does the light not make it here, the distance being too far to go past the gas and black holes and whatever in between? Or what?

If I could handle the math, maybe I could handle a star's passing better. Or, at least, sort of understand it. (Hey, just a gut feeling.)